Pitting corrosion is an insidious localized form of corrosion causing much devastating destruction to structural members such as stainless steel in chloride environment. This paper gives a review of the mechanism processes of pitting, stages, factors facilitating pitting corrosion, techniques of evaluating pitting corrosion and some research work on pitting corrosion. The rudimentary knowledge of the mechanisms of pitting corrosion from this work will be of assistance to the selection process, specification and the use of stainless steels and other structural members.

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Dedicated to the memory of my grandpa RÉSUMÉ Au cours des dernières années, les composites à matrice métallique (CMM) du type AI-B4C ont reçu une attention considérable en raison de leur légèreté, de leur conductivité thermique supérieure, de leur grande rigidité et de leur dureté. Grâce à la capacité particulière de l'isotope B 10 à agir comme capteurs des neutrons, les composites AI-B4C ont été utilisés par l'industrie nucléaire à titre de matériaux absorbeurs de neutrons pour la fabrication de la section interne de contenants de transport et de stockage des combustibles nucléaires périmés. Bien que l'incorporation de particules céramiques dans la matrice d'aluminium permet d'améliorer les propriétés physiques et mécaniques de l'alliage de base, elle peut également modifier son comportement en corrosion. En outre, en tant que matériau absorbeur de neutrons utilisé dans les contenants de transport et de stockage pour les combustibles nucléaires usés, en particulier pour les applications de stockage humide, les composites A1-B 4 C sont continuellement en contact avec l'eau du bassin du réacteur (l'un d'eux contenant de l'acide borique avec une concentration de B-2500 ppm), un milieu généralement considéré comme étant légèrement corrosif. Ainsi, pour des raisons de sécurité évidentes, il devient très important de comprendre leur comportement en corrosion dans un milieu d'acide borique. Cependant, à ce jour, force est de constater que très peu d'études ont été consacrées à la détermination de la tenue en corrosion des composites AI-B4C, et ce en particulier dans l'acide borique, contrairement au nombre considérable de travaux de recherche dédiés à la corrosion des composites Al-SiC et AI-AI2O3 dans divers environnements. Parmi la littérature traitant des phénomènes de corrosion, les solutions 3.5% NaCl et 0.5 M K2SO4 sont celles les plus couramment utilisées pour l'étude du comportement en corrosion des matériaux composites à matrice métallique. Par conséquent, la présente recherche a visé l'étude du comportement en corrosion des composites CMM du type AI-B4C dans trois solutions, soit H3BO3 contenant 2500 ppm B, 3.5% NaCl et 0.5 M K 2 SO 4. Parmi les solutions considérées, celle de NaCl a été identifiée comme étant celle induisant le plus de dommages au composite AI-B4C suivie, dans l'ordre, des solutions de K2SO4 et de H3BO3. Aucune corrosion appréciable n'a été observée dans les solutions d'acide borique et de K2SO4. Cependant, des piqûres apparentes ont été observées suite aux essais réalisés dans la solution de NaCl, et ce pour tous les matériaux étudiés. Pour l'alliage de base, le site préférentiel de piqûration était l'interface Al/Fe générée par la présence de particules intermétalliques. Pour le composite, l'interface AI/B4C était celle la plus favorable au développement de la corrosion localisée. Par ailleurs, il a été constaté que la 11 résistance à la corrosion des matériaux composites diminue lorsque la fraction volumique de B4C est augmentée. Dans le but de contrer l'agressivité des phénomènes de cor...

The pitting corrosion behavior of 301, 304 and 316 austenitic stainless steels in 2M H 2 SO 4 at 0-1.5% NaCl concentrations was investigated through potentiodynamic polarization and optical microscopy analysis. Electrochemical analysis of the pitting corrosion inhibition and surface protection properties of rosemary oil and aniline on the stainless was also performed. The corrosion rate, pitting potential, passivation potential, metastable pitting potential and surface morphology of both steels where significantly altered by changes in chloride concentration, differences in alloy composition and metallurgical properties of the steels. 316 steel had the lowest corrosion rate and highest pitting corrosion resistance followed by 301 steel. The surface morphology of 316 steel was slightly altered at 1.5% NaCl concentration while 301 steel appears to etch with grain boundaries appearing at higher chloride concentration. 304 steel showed no resistance to pitting after 0% NaCl coupled with relatively significant increase in corrosion rate values. Its surface morphology showed the presence of corrosion pits with respect to chloride and inhibitor concentration. Rosemary oil and aniline significantly reduced the corrosion rates values of the stainless steels and with consequent increase in their pitting corrosion resistance; however the compounds had no positive influence on the pitting corrosion behavior of 304 steel.

The built environment consumes a lot of energy and material. A huge demand of about 40 billion tonnes of aggregates is demanded for construction purpose. The cost of material accounts for more than 60% of the total project cost. However, 10% of construction material end up as demolition wastes yearly. Aggregate is a beneficial building component in construction. There is much need to develop ways to ensure it is utilized properly as construction and demolition waste contribute a large percent to landfills. This review of literature examined the generation of construction and demolition waste generated in developed countries, waste characterization, and utilization in pavement construction. Additionally, environmental, economic and social benefits of the reuse of this waste was espoused. The result of the review revealed that The initial construction material quality, scale of the project, contract and construction mode used affect the amount and quality of CDW. CDW are bulky and not suitable for composting and incineration. Ultimately, the utilization of this waste would reduce the amount of raw material used in construction leading to conservation. Also, there would be reduction in the energy cost associated with mining (quarrying), extraction and transportation of natural aggregates in track with the conservation of natural resources and the construction of cost-effective pavements.

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The influence of deanol on the corrosion behaviour of mild steel in dilute sulphuric acid with sodium chloride addition was studied by means of mass-loss, potentiodynamic polarization, electrode potential monitoring, scanning electron microscopy and statistical analysis. Results show that deanol performed excellently with a maximum inhibition efficiency of 97.9 % obtained from the mass loss technique and 98.23 % from the potentiodynamic polarization tests at the maximum deanol concentration evaluated. Polarization studies show that the amino alcohol is a cathodic type inhibitor. Adsorption of deanol on the steel surface was observed to obey the Langmuir and Frumkin adsorption isotherms. Scanning electron microscopy studies confirmed the corrosion protection property of deanol to be through adsorption on the mild steel surface while statistical evaluation showed the overwhelming influence and significance of inhibitor concentration on inhibition efficiency compared with exposure time. KEYWORDSOrganic compounds, metals, deanol, corrosion, sulphuric acid, inhibitor IntroductionMild steel has excellent mechanical properties. Its low cost allows for extensive use as the material of construction in petroleum industries, chemical processing plants, marine applications, boilers, refinery plants, extractive industries, etc. However, its application under these industrial conditions subjects it to rapid corrosion attack especially in applications involving the extensive use of sulfuric acid and other corrosive media due to their wide range of applications, including domestic acidic drain cleaner, electrolyte in lead-acid batteries and various cleaning agents.1 The most cost-effective and practical corrosion control technique for effectively preventing the occurrence or reducing the severity of corrosion is to alter the electrochemical nature of the environment with chemical compounds known as inhibitors.2,3 Effective corrosion inhibition is subject to the chemical composition, molecular structure and affinity of the inhibiting compound with the metallic alloy surface. Deanol has been used for corrosion prevention in concrete with mixed results. [4][5][6][7] The compound adsorbs through concrete resulting in the formation of a complex precipitate of protective film, which adsorbs onto the metal surface. This provides an impenetrable barrier to metal dissolution that acts to stifle cathodic and or anodic electrochemical corrosion reactions taking place at the metal/solution interface. This investigation aims to evaluate the corrosion inhibition properties of deanol on the electrochemical behaviour of mild steel in aqueous dilute sulphuric acid at ambient temperature of 25 °C.

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